The invention relates to a roller seam welding process and a roller seam resistance-welding machine for carrying out the process.
The use of roller seam welding machines, in particular for welding motor vehicle fuel tanks, is known. Two welding rollers, an upper and a lower, each fed with a wire electrode, follow the contour of the superimposed welding flanges of the tank halves, these flanges having been tacked together prior to welding. In particular, to weld tanks whose welding flanges lie in one plane, it is a known practice to provide a workpiece table to hold the tacked container, this table being provided with a contour, e.g. an outer contour, matching the tank-contour to be welded. The workpiece table is then moved along its contour, causing the welding flange of the tank secured to the table to move between the welding rollers, which are mounted in a fixed position on the machine. This way of moving the tank, with the table driven, in a known manner, by gear teeth on the table's outer contour with which a drive pinion engages, and with a driven arm (called a pantograph) engaging with the table to maintain the tangentiality of the contour to the welding direction, has provided an effective technique for welding tanks with a level welding flange.
The vehicle manufacturers are requiring increasingly complex tank shapes whose fabrication involves non-level tank parting faces, i.e. non-level welding flanges. To weld such tank shapes, technical development has hitherto concentrated on manipulating the tank accordingly, the welding flange still being guided past welding rollers mounted in a fixed position. In particular, to manipulate the tank, a workpiece table has been proposed which enables the tank to be tilted about a tilting axis (Japanese Utility Model 4-470). In addition, manipulation of the tank by means of an industrial robot has been proposed (DE-A 3603919). It has been found that with this method of welding the precise track of the welding path, specified with very close tolerances, often cannot be maintained. The three-dimensional movement of the tank is difficult to manage, particularly in the case of large and heavy tanks. The welding rate--which for efficient tank production should be as high as possible--may be impaired.
It is therefore an object of the invention to provide a process for the roller seam welding of tanks with complex shapes in which the welding flange does not lie in one plane. This should enable a precisely aligned welding path and a high welding rate to be achieved in the simplest possible manner.
It is also an object of the invention to provide a roller seam resistance-welding machine with which the process can be carried out. This machine should allow the welding path to be tracked in a way which is as simple as possible and yet extremely precise, should permit a high welding rate to be maintained, and should allow flanges which follow a three-dimensional profile to be welded at a high welding rate, even on large and heavy tanks.